Field of the Invention
The present invention relates to elements capable of controlling domain switching in irregular ferroelectric devices.
Domain switching is a switching phenomenon between two single-domain states for positive and negative polarizations, that is, a phenomenon involving polarization reversal.
The term irregular ferroelectrics is a general term for a ferroelectric substance of a nature such that the spontaneous strain switches from one orientation to another according to the state of polarization. Some of the crystals belonging to the point groups mm2, 2-I and 2-II are the ferroelectric crystal which falls under the category of irregular ferroelectric crystals. These irregular ferroelectric crystals are summarized in Table I below.
Table 1 ______________________________________ Point Group Ferroelectric Crystals ______________________________________ mm2 KH.sub.2 PO.sub.4, Gd.sub.2 (MoO.sub.4).sub.3, boracite 2-I 2-II rochelle salt, ammonium cadmium sulfate, methyl ammonium aluminum sulfate 12-hydrate ______________________________________
As will be evident from Table 1, crystals classified under the category irregular ferroelectrics are optically biaxial double refractive crystals. In an irregular ferroelectric crystal, polarization reversal causes a re-orientation of crystallographic axis. In a Gd.sub.2 (MoO.sub.4).sub.3 single crystal, for example, the ferroelectric axis is coincident with the c-axis, and the spontaneous polarization is parallel or contra-parallel with the c-axis according to polarity. Hence, when a threshold voltage is applied to this Gd.sub.2 (MoO.sub.4).sub.3 single crystal, the polarization is switched according to its polarity and, at the same time, this switching gives rise to a change in the crystal itself which is brought about by rotating the a-axis and b-axis on the c-axis through 90.degree.. With this change, the biaxial double refraction characteristic also changes.
If these switching and optical characteristics inherent in the irregular ferroelectric crystal are utilized, a highly useful bistable optical switch can be realized by suitably growing, stopping growing or extinguishing the single domain which has a specific polarity in the irregular ferroelectric single crystal plate.